Suppose seismologists studying faults near an urbanized area could state with empirical reliability that a major earthquake is 100 to 1,000 times more likely to occur in the upcoming week than during a typical seven-day period. What actions, if any, should be taken for civil protection? Should the forecast be publicly broadcast? How should the public be advised to use such information? These quandaries deserve thoughtful consideration, because we have entered the era of operational earthquake forecasting.

The goal of operational earthquake forecasting is to provide the public with authoritative information on the time dependence of regional seismic hazards. We...